1. Field of the Invention
The present invention relates to a temperature control system for a machine tool that performs nanometer-order machining.
2. Description of Related Art
In an ultra-precision machine, such as a machine tool or a measuring device for nanometer-order machining or measurement, the ambient temperature influences the machining accuracy and measurement accuracy, thereby changing the machined or measured shape. High-precision temperature control is needed to suppress the influence of the ambient temperature.
In a machine tool shown in FIG. 8, the interior of a mechanical section 2 is networked with a channel for gas bearings. For precision machining, the mechanical section 2 and a controller 14 are installed in an air-conditioned room 15, and a partition 17 for the safety of an operator 16 is provided around them. The temperature of gas supplied to the gas bearings is kept constant by a temperature controller 6. The temperature controller 6 is provided with a mechanism that is supplied with gas such as compressed air from a compressor 18 and serves to heat and cool the supplied gas (see JP2004-255494A).
In order to keep the temperature of the gas for the gas bearings constant, as shown in FIG. 2, the gas temperature is detected by a temperature sensor 10a that is located in the temperature controller 6 or near its gas outlet and fed back to the temperature controller 6 to maintain the constant gas temperature.
In this system, the temperature sensor 10a of the temperature controller 6 is not configured to detect the temperature around the machine tool 1, so that it cannot be easily influenced by a slight temperature change around the machine tool. However, the controller 6 cannot cope with a substantial temperature change around the machine tool 1.
If a temperature sensor 10b is set on the surface of or inside the machine tool mechanical section 2, as shown in FIG. 3, the temperature of the gas for the gas bearings is controlled according to the temperature change of the mechanical section 2.
In general, however, the heat capacity of the machine tool mechanical section 2 is very large. If a temperature change is caused around the machine tool 1 or in the mechanical section 2 in the configuration of FIG. 3, therefore, it takes a very long time before the temperature can be kept constant by the temperature controller 6 and the gas for the gas bearings. Thus, satisfactory temperature control cannot be performed if the time constant is so large that the heat capacity of the machine tool mechanical section 2 is too large for the gas.
If the temperature inside the machine tool cover 3 is detected by means of a temperature sensor 10c that is located in a position inside the cover 3 and off the machine tool mechanical section 2, as shown in FIG. 4, the gas of which the temperature is detected by the temperature sensor 10c is gas that is discharged from the mechanical section 2 into the space inside the machine tool cover 3 after a bearing portion is passed by the gas having passed through a gas bearing channel 4.
In this case, the temperature inside the machine tool cover 3 that is measured by the temperature sensor 10c can be controlled to be fixed in coincidence with a target temperature. Since the gas that is supplied to the gas bearing changes the temperature to establish this state, however, the temperature of the mechanical section 2 also changes. Thus, the temperature change of the mechanical section 2 cannot be suppressed, that is, an original purpose cannot be achieved.
The machine tool is a large metal mass of which the heat capacity is too large, as mentioned before, so that its temperature control is easily retarded. To cope with this, anticipative temperature control should preferably be performed by forecasting a future temperature change of the machine tool mechanical section, based on the temperature of any other small-capacity portion than the mechanical section.
However, the temperature control of the machine tool mechanical section is difficult mainly because the temperature of the machine tool depends on both the respective temperatures of air inside the machine tool cover and the gas for the gas bearings, and because both these temperatures influence each other in a ratio appropriate to each individual machine tool.